I'm wondering if you start with a 408 with 11:1 compression and a 408 with 9:1 compression, and you run the same fuel (91 octane), and same supercharger, which would have better results?

Obviously you could run more boost and timing within the limits of the 91 octane in the lower compression motor. But would the bump in compression produce more power with less boost/timing?

 

My feeling is with such high static compression on the 11:1 motor no matter what boost they are both running detonation will be a BIG issue with it. The lower compression 9:1 motor would fair much better an would allow more boost=more hp and tq..11:1 is really too high static comp. for boost. A better way to compare the 2 engine might be which is better a normally aspirated 11:1 408 or a 9:1 boosted 408.

 

I think you would have to limit boost on either setup, but the lower comp motor would allow for more timing at the same boost level and be more efficient and less likely to detonate. Power should be similar if the tune is done right.

 

There is no comparison to those two motors. Boosted 408 would make much more power.

LS2's run 10.9 compression and can easily take 8psi without detination. Has no one run this test before?

 

the 9.1 motor would make more power all things being equal cause of being able to run more timing/boost. the 11.1 motor could make more power IF it had a spec'ed cam in it. i had a 11.1 351w in my fox and stuck a turbo on it with a custom stick and made 632rwhp/700rwtq maxing the turbo out. that was using 92 octane and a fmic

 

That's what I'm thinking I should do. Get a custom cam that will bring down my compression enough to run an innercooled tvs2300.

 

He's talking about both motors being the same, both a boosted 408. The differences being compression and what it limits. With a 9.1:1 motor you can run more boost and timing without detonation. Yea you can run 8-10psi on a stock LS2 with 10.9:1 compression but you can get away with 18psi and more timing on a 9.1:1 motor. There's a lot of variables that would make it hard to test. My bet is on the max effort 9.1:1 motor making more power though.

 

alot will also depend on who is tuning it. the tuning window with thehigher comp is a good bit smaller so you have to be careful.

 

if you keep the motor out of detonation the 11-1 compression will kick the crap outa the 9-1 motor all day long....

 

Id run e85 with that 11.1 or race gas mixture. you wont be able to run much boost with 91 oct on that cr without running into detonation.

 

at the same boost levels the higher compression motor will make more power.

 

Yes true but I'm not asking that. If the high comp motor can safely run 8 psi without detination, and the lower comp motor can safely run 13psi, which would make more power?

I know I can run 8 psi but probably not much more than that on pump gas. We have E85 in Vegas but i spend half the year in Utah where they don't have anything but pump gas.

 

Lower comp like 9.6:1, 18psi, Pump gas + methanol and you'll be just fine.

 

this is what i was sayng in my first post all else being equal the lower comp motor can run more boost/timing and WILL make more power

 

the lower compression motor.

because it possible to fit more air and fuel in the cylinder.

 

Im running 11-1 comp on my 408 with my kennebell 2.8 making 10lbs of boost . Im running only running 91 with low timming but this setup kicks *** its very responsive

Also with hi comp you dont need alot of boost to make to make alot of power

 

Your more limited as well though. With lower comp you can always turn the boost up more. Your not going to see a 11.1:1 motor running 10psi on a pump tune make as much as a 9.6:1 motor running 18psi and a pump tune. It all depends on what the end goal is and what he wants. Lower compression is less chance of having a big problem. If he was going to run E-85 or race gas I'd say go for it but he stated he wants to stay on pump gas. His best option while staying on the safer side is a lower comp engine with more boost and maybe methanol if he wants.

 

How big of an intercooler do you run on this set up?

 

He most likely runs a KB aftercooler...there's really no way to intercool a positive displacement blower....they usually run aftercoolers on the underside of the blower with a water pump to a heat exchanger. Their as efficient as it really gets with a bigger twin screw.

 

Ah, I see, thanks, I'm not real familiar with those KB's.